Cut-off, and why dribbling is a design fault
A pot dribbles when liquid clings to the outside of the spout instead of breaking away cleanly at the end of a pour. The properties that govern this are the sharpness of the spout lip, whether the underside is undercut, and how smooth the interior of the spout is. A thick rounded spout lip is the usual culprit. This is not a cosmetic complaint: a dribbling pot forces you to pour faster than the steep wants, and it puts hot tea on your hand and the table every single time.
Emptying completely
Any liquid left in the pot at the end of a pour keeps extracting the leaf, so the next infusion starts from an over-brewed base. In short-steep brewing this is the single most common cause of a session going harsh by the fourth or fifth infusion. Check three things: whether the pot pours to genuinely dry when fully inverted, whether the strainer sits low enough that liquid does not pool behind it, and whether the internal step at the base of the spout traps a spoonful. A pot that keeps a residue is not unusable — you simply have to shake it out and know that you must.
The lid, the air hole and the seal
A lid needs to fit closely enough to hold the leaf back when the pot is tipped and loosely enough to let air in behind the pour. The air hole in the lid is what makes the second possible; a blocked hole makes a pot glug and pour unevenly, and covering the hole with a finger is the standard way to stop the flow instantly, which is a useful trick and a good test of how well the lid seats. A lid that rocks will fall into the tea when you tip the pot far. A lid ground to a perfect seal will lock on when the pot is hot, because the body expands.
Filter placement
Where the filter sits decides how much of the leaf bed the water can reach and how fast the pot empties. A single small hole at the base of the spout blocks with anything but coarse leaf. A ball or plate of holes is better. A wall-wide ceramic mesh, as in a Japanese pot, is best of all and is the reason such pots handle fine steamed leaf that would stop anything else. A drop-in basket is the weakest arrangement because it also confines the leaf, which is a different problem stacked on the same object.
Handle position, weight and where the heat is
A side handle keeps the hand clear of the steam rising from the lid, which is why it dominates in Japanese pots poured with one hand. A rear handle gives leverage for a heavier pot. A bail handle over the top keeps the hand furthest from a body full of boiling water. None of these is better; each answers a different weight and a different pour. The thing to test is a full pot, not an empty one — an empty pot tells you nothing about where the balance goes when it is loaded.
How to test a pot you cannot fill
In a shop, look down the spout for a smooth bore and a clean lip, check the lid for a close but not locking fit, find the air hole, look at the filter from inside, and tip the pot to see whether the lid stays put. If water is available, pour a full one and watch the last of the stream. These take under a minute and they are the properties you will interact with every day, unlike the clay, which you will think about once.